0.14.7 crash

[Roguelazer]

Tried upgrading from 0.14.3 to 0.14.7 and graphite crashes with the following:

Traceback (most recent call last):
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/graphite/metrics/views.py", line 128, in find_view
    leaves_only=leaves_only,
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/graphite/storage.py", line 264, in find
    for match in self._find(query):
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/graphite/storage.py", line 295, in _find
    for node in result or []:
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/biggraphite/plugins/graphite.py", line 375, in find_nodes
    results = self._find_glob(query, leaves_only, start_time, end_time)
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/biggraphite/plugins/graphite.py", line 418, in _find_glob
    end_time=end_time,
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/biggraphite/glob_utils.py", line 330, in graphite_glob
    directories = accessor.glob_directory_names(graphite_glob, start_time, end_time)
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/biggraphite/drivers/cassandra.py", line 1792, in glob_directory_names
    tracing.add_attr_to_trace("glob", glob)
  File "/srv/biggraphite-graphite-backend/venv/lib/python3.6/site-packages/biggraphite/tracing.py", line 61, in add_attr_to_trace
    tracer = execution_context.get_opencensus_tracer()
AttributeError: 'NoneType' object has no attribute 'get_opencensus_tracer'

I think this is straightforward to fix.